U.S. patent number 11,237,469 [Application Number 16/820,922] was granted by the patent office on 2022-02-01 for wavelength conversion element, light source device, and projector.
This patent grant is currently assigned to SEIKO EPSON CORPORATION. The grantee listed for this patent is SEIKO EPSON CORPORATION. Invention is credited to Toshiaki Hashizume.
United States Patent |
11,237,469 |
Hashizume |
February 1, 2022 |
Wavelength conversion element, light source device, and
projector
Abstract
The wavelength conversion element includes a phosphor layer
having a plurality of phosphor particles and a binder configured to
bind one of the phosphor particles adjacent to each other and
another of the phosphor particles adjacent to each other out of the
plurality of phosphor particles, an antireflection layer disposed
on an incident side of the excitation light with respect to the
phosphor layer, and a substrate provided with the phosphor layer,
wherein the binder includes glass, and the binder binds a part of a
surface of the one of the phosphor particles and a part of a
surface of the another of the phosphor particles to each other.
Inventors: |
Hashizume; Toshiaki (Okaya,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
SEIKO EPSON CORPORATION |
Tokyo |
N/A |
JP |
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Assignee: |
SEIKO EPSON CORPORATION (Tokyo,
JP)
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Family
ID: |
1000006086771 |
Appl.
No.: |
16/820,922 |
Filed: |
March 17, 2020 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20200301261 A1 |
Sep 24, 2020 |
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Foreign Application Priority Data
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Mar 18, 2019 [JP] |
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JP2019-050086 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03B
21/204 (20130101) |
Current International
Class: |
H05B
33/10 (20060101); G03B 21/20 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2015-197474 |
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Nov 2015 |
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JP |
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2017-111176 |
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Jun 2017 |
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JP |
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Primary Examiner: Coughlin; Andrew J
Attorney, Agent or Firm: Oliff PLC
Claims
What is claimed is:
1. A wavelength conversion element comprising: a phosphor layer
having a plurality of phosphor particles and a binder that binds
one of the phosphor particles adjacent to another one of the
phosphor particles; an antireflection layer on a side of the
phosphor layer where excitation light is incident; and a substrate
provided with the phosphor layer, wherein the binder includes
glass, the binder binds a part of a surface of the one of the
phosphor particles and a part of a surface of the other one of the
phosphor particles to each other, and each of the one of the
phosphor particles and the other one of the phosphor particles has
part of the surface which is not bound to the binder.
2. The wavelength conversion element according to claim 1, wherein
a proportion of a volume of the binder to a total volume of a sum
of volumes of the phosphor particles and a sum of volumes of the
binder is larger than 0 vol % and no larger than 10 vol %.
3. A light source device comprising: the wavelength conversion
element according to claim 2; and a light source configured to emit
excitation light to the wavelength conversion element.
4. A projector comprising: the light source device according to
claim 3; a light modulation device configured to modulate light
emitted from the light source device in accordance with image
information; and a projection optical device configured to project
the light modulated by the light modulation device.
5. A light source device comprising: the wavelength conversion
element according to claim 1; and a light source configured to emit
excitation light to the wavelength conversion element.
6. A projector comprising: the light source device according to
claim 5; a light modulation device configured to modulate light
emitted from the light source device in accordance with image
information; and a projection optical device configured to project
the light modulated by the light modulation device.
7. The wavelength conversion element according to claim 1, wherein
each of the one of the phosphor particles and the other one of the
phosphor particles has part of the surface which is not bound to
the binder due to voids in the binder.
8. A wavelength conversion element comprising: a phosphor layer
having a plurality of phosphor particles, a binder, and a
respective antireflection layer on a surface of each of the
plurality of phosphor particles; and a substrate provided with the
phosphor layer, wherein the binder includes glass, the binder binds
a part of the antireflection layer on the surface of one of the
phosphor particles and a part of the antireflection layer on the
surface of the other of the phosphor particles to each other, and
each of the one of the phosphor particles and the other one of the
phosphor particles has part of the surface which is not bound to
the binder.
9. The wavelength conversion element according to claim 8, wherein
a proportion of a volume of the binder to a total volume of a sum
of volumes of the phosphor particles and a sum of volumes of the
binder is larger than 0 vol % and no larger than 10 vol %.
10. A light source device comprising: the wavelength conversion
element according to claim 9; and a light source configured to emit
excitation light to the wavelength conversion element.
11. A projector comprising: the light source device according to
claim 10; a light modulation device configured to modulate light
emitted from the light source device in accordance with image
information; and a projection optical device configured to project
the light modulated by the light modulation device.
12. A light source device comprising: the wavelength conversion
element according to claim 8; and a light source configured to emit
excitation light to the wavelength conversion element.
13. A projector comprising: the light source device according to
claim 12; a light modulation device configured to modulate light
emitted from the light source device in accordance with image
information; and a projection optical device configured to project
the light modulated by the light modulation device.
14. The wavelength conversion element according to claim 8, wherein
each of the one of the phosphor particles and the other one of the
phosphor particles has part of the surface which is not bound to
the binder due to voids in the binder.
15. A wavelength conversion element comprising: a phosphor layer
having a plurality of phosphor particles, a binder, and a
respective antireflection layer on a surface of each of the
plurality of phosphor particles; and a substrate provided with the
phosphor layer, wherein the binder includes glass, the binder binds
a part of the surface of a first one of the phosphor particles and
a part of the antireflection layer on the surface of a second one
of the phosphor particles to each other, and each of the first one
of the phosphor particles and the second one of the phosphor
particles has part of the surface which is not bound to the
binder.
16. The wavelength conversion element according to claim 15,
wherein the binder binds a part of the surface of a third one of
the phosphor particles and a part of the surface of a fourth one of
the phosphor particles to each other, and each of the third one of
the phosphor particles and the fourth one of the phosphor particles
has part of the surface which is not bound to the binder.
17. The wavelength conversion element according to claim 15,
wherein each of the one of the phosphor particles and the other one
of the phosphor particles has part of the surface which is not
bound to the binder due to voids in the binder.
18. A light source device comprising: the wavelength conversion
element according to claim 15; and a light source configured to
emit excitation light to the wavelength conversion element.
19. A projector comprising: the light source device according to
claim 18; a light modulation device configured to modulate light
emitted from the light source device in accordance with image
information; and a projection optical device configured to project
the light modulated by the light modulation device.
Description
The present application is based on, and claims priority from JP
Application Serial Number 2019-050086, filed Mar. 18, 2019, the
disclosure of which is hereby incorporated by reference herein in
its entirety.
BACKGROUND
1. Technical Field
The present disclosure relates to a wavelength conversion element,
a light source device, and a projector.
2. Related Art
In the past, there has been known a wavelength conversion element
which is excited by excitation light entering the wavelength
conversion element to emit fluorescence having longer wavelength
than the wavelength of the excitation light. As such a wavelength
conversion element, there has been known a light emitting element
provided with a base member, a reflecting layer formed on a surface
of the base member, and a phosphor layer formed on the reflecting
layer (see, e.g., JP-A-2015-197474 (Document 1)).
In the light emitting element described in Document 1, the phosphor
layer has a plurality of phosphor particles and a binder for
binding the plurality of phosphor particles to each other.
The binder includes a cross-linked body made of an inorganic
material such as liquid glass. The binder binds a phosphor particle
to another phosphor particle adjacent to each other, and at the
same time, binds the phosphor particles and the surface of the
reflecting layer with each other. The phosphor particles are each a
phosphor shaped like a particle which absorbs the excitation light
emitted from the outside to emit the fluorescence. The phosphor
particles include a phosphor material such as a YAG series
material. Further, in Document 1, there is shown an example in
which a light source device having the light emitting element
described above is applied to a projector.
In the phosphor layer described in Document 1, the plurality of
phosphor particles is encapsulated in the binder. In other words,
the binder exists around the phosphor particles so as to cover the
entire surface of each of the phosphor particles. Therefore, the
fluorescence emitted from the phosphor particles enters the inside
of the binder, propagates in the binder, and is then emitted from
the phosphor layer. The fluorescence emitted from the phosphor
layer is emitted from the light source device, and then enters a
reflective liquid crystal panel constituting an optical system.
However, when the fluorescence propagates inside the binder in the
phosphor layer, an exit area of the fluorescence in the surface of
the phosphor layer becomes larger than the incident area of the
excitation light. Further, when the exit area of the fluorescence
is large, there is a possibility that the incident efficiency of
the fluorescence to the liquid crystal panel decreases in the
optical system. In other words, when the entire surface of the
phosphor particle is covered with the binder, there is a
possibility that the use efficiency of the fluorescence in the
optical system which the fluorescence enters from the phosphor
layer decreases.
In contrast, in the wavelength conversion element, there can occur
a phenomenon called backward scattering (backscatter) that a part
of the excitation light with which the phosphor layer has been
irradiated returns without being converted into the fluorescence by
the phosphor particles. There is a problem that the wavelength
conversion efficiency of the excitation light decreases when the
intensity of such excitation light increases.
SUMMARY
A wavelength conversion element according to a first aspect of the
present disclosure includes a phosphor layer having a plurality of
phosphor particles and a binder configured to bind one of the
phosphor particles adjacent to each other and another of the
phosphor particles adjacent to each other out of the plurality of
phosphor particles, an antireflection layer disposed on an incident
side of the excitation light with respect to the phosphor layer,
and a substrate provided with the phosphor layer, wherein the
binder includes glass, and the binder binds a part of a surface of
the one of the phosphor particles and a part of a surface of the
another of the phosphor particles to each other.
A wavelength conversion element according to a second aspect of the
present disclosure includes a phosphor layer having a plurality of
phosphor particles, a binder configured to bind one of the phosphor
particles adjacent to each other and another of the phosphor
particles adjacent to each other out of the plurality of phosphor
particles, and an antireflection layer disposed on a surface of the
phosphor particle, and a substrate provided with the phosphor
layer, wherein the binder includes glass, and the binder binds at
least any one of a part of a surface of the one of the phosphor
particles and a part of a surface of the another of the phosphor
particles, the antireflection layer disposed on the surface of the
one of the phosphor particles and the antireflection layer disposed
on the surface of the another of the phosphor particles, and a part
of the surface of the one of the phosphor particles and the
antireflection layer disposed on a part of the surface of the
another of the phosphor particles.
In the first and second aspects described above, a proportion of a
volume of the binder to a total volume of a sum of volumes of the
phosphor particles and a sum of volumes of the binder may be larger
than 0 vol % and no larger than 10 vol %.
A light source device according to a third aspect of the present
disclosure includes any one of the wavelength conversion elements
described above, and a light source configured to emit excitation
light to the wavelength conversion element.
A projector according to a fourth aspect of the present disclosure
includes the light source device described above, a light
modulation device configured to modulate light emitted from the
light source device in accordance with image information, and a
projection optical device configured to project the light modulated
by the light modulation device.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram showing a configuration of the
projector according to the first embodiment.
FIG. 2 is a schematic diagram showing a configuration of a light
source device in the first embodiment.
FIG. 3 is a plan view of a wavelength conversion element in the
first embodiment viewed from an incident side of excitation
light.
FIG. 4 is a schematic diagram showing a cross-sectional surface of
the wavelength conversion element in the first embodiment.
FIG. 5 is a schematic diagram showing a part of a phosphor layer
and an antireflection layer in the first embodiment in an enlarged
manner.
FIG. 6 is a schematic diagram showing a binding state of phosphor
particles with a binder in the first embodiment.
FIG. 7 is a graph showing brightness and spread of light in an
optical system with respect to the area of the binding part in the
first embodiment.
FIG. 8 is a graph showing a relationship between a glass content
rate and optical system efficiency in the first embodiment.
FIG. 9 is a diagram of an image showing a phosphor layer the glass
content rate of which is 30 vol %, and which is formed at the
calcination temperature of 1000.degree. C. in the first
embodiment.
FIG. 10 is a diagram of an image showing a phosphor layer the glass
content rate of which is 20 vol %, and which is formed at the
calcination temperature of 1000.degree. C. in the first
embodiment.
FIG. 11 is a diagram of an image showing a phosphor layer the glass
content rate of which is 10 vol %, and which is formed at the
calcination temperature of 1000.degree. C. in the first
embodiment.
FIG. 12 is a diagram of an image showing a phosphor layer the glass
content rate of which is 5 vol %, and which is formed at the
calcination temperature of 1000.degree. C. in the first
embodiment.
FIG. 13 is a diagram of an image showing a phosphor layer the glass
content rate of which is 3 vol %, and which is formed at the
calcination temperature of 1000.degree. C. in the first
embodiment.
FIG. 14 is a flowchart showing a method of manufacturing the
wavelength conversion element in the first embodiment.
FIG. 15 is a graph showing a relationship between the calcination
temperature and the viscosity of the glass in the first
embodiment.
FIG. 16 is a diagram of an image showing a phosphor layer the glass
content rate of which is 5 vol %, and which is formed at the
calcination temperature of 750.degree. C. in the first
embodiment.
FIG. 17 is a diagram of an image showing a phosphor layer the glass
content rate of which is 5 vol %, and which is formed at the
calcination temperature of 800.degree. C. in the first
embodiment.
FIG. 18 is a diagram of an image showing a phosphor layer the glass
content rate of which is 5 vol %, and which is formed at the
calcination temperature of 850.degree. C. in the first
embodiment.
FIG. 19 is a diagram of an image showing a phosphor layer the glass
content rate of which is 5 vol %, and which is formed at the
calcination temperature of 900.degree. C. in the first
embodiment.
FIG. 20 is a diagram of an image showing a phosphor layer the glass
content rate of which is 5 vol %, and which is formed at the
calcination temperature of 950.degree. C. in the first
embodiment.
FIG. 21 is a schematic diagram showing a cross-sectional surface of
a wavelength conversion element provided to a projector according
to a second embodiment.
FIG. 22 is a schematic diagram showing a binding state of a
plurality of phosphor particles and a binder in the second
embodiment.
FIG. 23 is a schematic diagram showing a binding state of the
phosphor particles with a binder in the second embodiment.
FIG. 24 is a flowchart showing a method of manufacturing the
wavelength conversion element in the second embodiment.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
First Embodiment
A first embodiment of the present disclosure will hereinafter be
described based on the drawings.
Schematic Configuration of Projector
FIG. 1 is a schematic diagram showing a configuration of a
projector 1 according to the present embodiment.
The projector 1 according to the present embodiment modulates the
light emitted from a light source device 4 described later to
project image light for forming an image corresponding to image
information on a projection target surface such as a screen in an
enlarged manner. As shown in FIG. 1, the projector 1 is provided
with an exterior housing 2 forming an exterior, and the light
source device 4 and an optical device 30 disposed inside the
exterior housing 2. It should be noted that a configuration of the
light source device 4 and the optical device 30 will be described
later in detail. Besides the above, although not shown in the
drawing, the projector 1 is provided with a control device for
controlling an operation of the projector 1, a power supply device
for supplying electronic components with electrical power, and a
cooling device for cooling a cooling target.
Configuration of Exterior Housing
The exterior housing 2 has a top surface part and a bottom surface
part each not shown, a front surface part 21, a back surface part
22, a left side surface part 23, and a right side surface part 24,
and is formed to have a substantially rectangular solid shape.
The front surface part 21 has an opening part 211 for exposing a
part of a projection optical device 36 described later, and the
image light to be projected by the projection optical device 36
passes through the opening part 211. Further, the front surface
part 21 has an exhaust port 212 from which a cooling gas having
cooled the cooling target in the projector 1 is discharged to the
outside of the exterior housing 2. Further, the right side surface
part 24 has an introduction port 241 from which a gas located
outside the exterior housing 2 is introduced inside as the cooling
gas.
Configuration of Optical Device
The optical device 30 is provided with a homogenizing device 31, a
color separation device 32, a relay device 33, an image forming
device 34, an optical component housing 35, and the projection
optical device 36.
The homogenizing device 31 homogenizes the light emitted from the
light source device 4. The light thus homogenized by the
homogenizing device 31 illuminates modulation areas of light
modulation devices 343 described later of the image forming device
34 via the color separation device 32 and the relay device 33. The
homogenizing device 31 is provided with two lens arrays 311, 312, a
polarization conversion element 313, and a superimposing lens
314.
The color separation device 32 separates the light having entered
the color separation device 32 from the homogenizing device 31 into
colored light beams of red, green, and blue. The color separation
device 32 is provided with two dichroic mirrors 321, 322 and a
reflecting mirror 323 for reflecting the blue light beam having
been separated by the dichroic mirror 321.
The relay device 33 is disposed on a light path of the red light
beam longer than a light path of the blue light beam and a light
path of the green light beam to suppress a loss of the red light
beam. The relay device 33 is provided with an incident side lens
331, relay lenses 333, and reflecting mirrors 332, 334.
It should be noted that although the relay device 33 is disposed in
the light path of the red light beam, this is not a limitation, and
it is also possible to adopt a configuration in which, for example,
the colored light beam longer in light path than other colored
light beams is set to the blue light beam, and the relay device 33
is disposed on the light path of the blue light beam.
The image forming device 34 modulates each of the colored light
beams of red, green, and blue having entered the image forming
device 34, and combines the colored light beams thus modulated with
each other to form the image light to be projected by the
projection optical device 36. The image forming device 34 is
provided with three field lenses 341, three incident side
polarization plates 342, three light modulation devices 343, and
three exit side polarization plates 344 each disposed in accordance
with the respective colored light beams entering the image forming
device 34, and a single color combining device 345.
The light modulation devices 343 each modulate the light emitted
from the light source device 4 in accordance with the image
information. The light modulation devices 343 include the light
modulation device 343R for modulating the red light beam, the light
modulation device 343G for modulating the green light beam, and the
light modulation device 343B for modulating the blue light beam. In
the present embodiment, the light modulation devices 343 are each
formed of a transmissive liquid crystal panel, and the incident
side polarization plate 342, the light modulation device 343, and
the exit side polarization plate 344 constitute a liquid crystal
light valve.
The color combining device 345 combines the colored light beams
respectively modulated by the light modulation devices 343B, 343G,
and 343R with each other to form the image light described above.
In the present embodiment, the color combining device 345 is formed
of a cross dichroic prism, but this is not a limitation, and it is
also possible for the color combining device 346 to be constituted
by, for example, a plurality of dichroic mirrors.
The optical component housing 35 houses the homogenizing device 31,
the color separation device 32, the relay device 33, and the image
forming device 34 each described above inside. It should be noted
that an illumination light axis Ax as a design optical axis is set
in the optical device 30, and the optical component housing 35
holds the homogenizing device 31, the color separation device 32,
the relay device 33, and the image forming device 34 at
predetermined positions on the illumination light axis Ax. The
light source device 4 and the projection optical device 36 are
disposed at predetermined positions on the illumination light axis
Ax.
The projection optical device 36 projects the image light entering
the projection optical device 36 from the image forming device 34
on the projection target surface in an enlarged manner. In other
words, the projection optical device 36 projects the light beams
having respectively been modulated by the light modulation devices
343B, 343G, and 343R. The projection optical device 36 is
configured as a combination lens having, for example, a plurality
of lenses housed in a lens tube having a cylindrical shape.
Configuration of Light Source Device
FIG. 2 is a schematic diagram showing a configuration of the light
source device 4.
The light source device 4 emits illumination light LT for
illuminating the light modulation devices 343 to the homogenizing
device 31. As shown in FIG. 2, the light source device 4 is
provided with a light source housing CA, and a light source section
41, an afocal optical element 42, a first retardation element 43, a
homogenizer optical element 44, a polarization split element 45, a
first light collection element 46, a second retardation element 47,
a second light collection element 48, a diffusely reflecting device
49, and a wavelength conversion device 5 each housed in the light
source housing CA.
The light source housing CA is a sealed housing difficult for dust
or the like to enter the inside thereof.
The light source section 41, the afocal optical element 42, the
first retardation element 43, the homogenizer optical element 44,
the polarization split element 45, the second retardation element
47, the second light collection element 48, and the diffusely
reflecting device 49 are arranged on an illumination light axis Ax1
set in the light source device 4.
The wavelength conversion device 5, the first light collection
element 46, and the polarization split element 45 are arranged on
an illumination light axis Ax2 which is set in the light source
device 4, and is perpendicular to the illumination light axis Ax1.
The illumination light axis Ax2 coincides with the illumination
light axis Ax at the position of the lens array 311. In other
words, the illumination light axis Ax2 is set on an extended line
of the illumination light axis Ax.
Configuration of Light Source Section
The light source section 41 is provided with a light source 411 for
emitting the light, and collimator lenses 414.
The light source 411 is provided with a plurality of solid-state
light sources 412 as the light emitting elements, and a support
member 413.
The solid-state light sources 412 are each a semiconductor laser
for emitting blue light L1s, which is s-polarized light as
excitation light. The blue light L1s is, for example, a laser beam
with a peak wavelength of 440 nm.
The support member 413 supports the plurality of solid-state light
sources 412 arranged in an array on a plane perpendicular to the
illumination light axis Ax1. The support member 413 is a metallic
member having thermal conductivity.
The blue light L1s having been emitted from the solid-state light
source 412 is collimated into a parallel light beam by the
collimator lens 414, and the parallel light beam enters the afocal
optical element 42.
It should be noted that in the present embodiment, the light source
411 has a configuration of emitting the blue light L1s which is
s-polarized light as linearly polarized light beams the same in
polarization direction. However, this is not a limitation, and the
light source 411 can also be provided with a configuration of
emitting blue light which is linearly polarized light beams
different in polarization direction. In this case, the first
retardation element 43 can be omitted.
Configuration of Afocal Optical Element
The afocal optical element 42 adjusts the beam diameter of the blue
light L1s which enter the afocal optical element 42 from the light
source section 41, and then makes the blue light L1s enter the
first retardation element 43. The afocal optical element 42 is
constituted by a lens 421 for collecting the incident light, and a
lens 422 for collimating the light beam collected by the lens
421.
Configuration of First Retardation Element
The first retardation element 43 is disposed on the light path
between the afocal optical element 42 and the homogenizer optical
element 44, more specifically, between the lens 422 and a
multi-lens array 441 constituting the homogenizer optical element
44. The first retardation element 43 is disposed so as to be able
to rotate along a surface which the blue light L1s enters, namely a
plane perpendicular to the illumination light axis Ax1. The first
retardation element 43 is formed of a 1/2 wave plate with respect
to the wavelength 446 nm of the blue light L1s. The optical axis of
the first retardation element 43 crosses the polarizing axis of the
blue light L1s entering the first retardation element 43. It should
be noted that the optical axis of the first retardation element 43
can be either of a fast axis and a slow axis of the first
retardation element 43.
The blue light L1s is coherent s-polarized light. Although the blue
light L1s is originally the s-polarized light, the polarization
axis of the blue light L1s crosses the optical axis of the first
retardation element 43. Therefore, when the blue light L1s is
transmitted through the first retardation element 43, the
s-polarized light is partially converted into p-polarized light.
Therefore, the blue light having been transmitted through the first
retardation element 43 becomes light including the blue light L1s
as the original s-polarized light and blue light L2p as the
p-polarized light are mixed in a predetermined proportion.
It should be noted that it is also possible for the light source
device 4 to be provided with a motor for rotating the first
retardation element 43.
Configuration of Homogenizer Optical Element
The homogenizer optical element 44 homogenizes the illuminance
distribution of the blue light L1s, L2p. The homogenizer optical
element 44 is formed of a pair of multi-lens arrays 441, 442.
Configuration of Polarization Split Element
The blue light L1s, L2p having passed through the homogenizer
optical element 44 enters the polarization split element 45.
The polarization split element 45 is a prism-type polarization beam
splitter, and separates an s-polarization component and a
p-polarization component included in the incident light from each
other. Specifically, the polarization split element 45 reflects the
s-polarization component, and transmits the p-polarization
component. Further, the polarization split element 45 has a color
separation characteristic of transmitting light with the wavelength
no shorter than a predetermined wavelength irrespective of whether
the polarization component is the s-polarization component or the
p-polarization component. Therefore, the blue light L1s as the
s-polarized light is reflected by the polarization split element
45, and then enters the first light collection element 46.
Meanwhile, the blue light L2p as the p-polarized light is
transmitted through the polarization split element 45, and then
enters the second retardation element 47.
Configuration of First Light Collection Element
The first light collection element 46 converges the blue light L1s
having been reflected by the polarization split element 45 on the
wavelength conversion device 5. Further, the first light collection
element 46 collimates fluorescence YL entering the first light
collection element 46 from the wavelength conversion device 5.
Although the first light collection element 46 is constituted by
two lenses 461, 462 in the example shown in FIG. 2, the number of
the lenses constituting the first light collection element 46 does
not matter.
Configuration of Wavelength Conversion Device
The wavelength conversion device 5 is excited by the light entering
the wavelength conversion device 5, and emits light having a
wavelength different from the wavelength of the light having
entered the wavelength conversion device 5 to the first light
collection element 46. In other words, the wavelength conversion
device 5 converts the wavelength of the incident light.
In the present embodiment, the wavelength conversion device 5 is
provided with a wavelength conversion element 51 for emitting the
fluorescence YL having the wavelength longer than the wavelength of
the blue light L1s in response to incidence of the blue light L1s
as the excitation light, and a rotary section RT for rotating the
wavelength conversion element 51 around a rotational axis Rx
parallel to the illumination light axis Ax2 as a predetermined
rotational axis. It should be noted that the rotational axis Rx of
the wavelength conversion element 51 is a rotational axis along the
incident direction of the blue light L1s as the excitation
light.
Among these, the wavelength conversion element 51 is a reflective
wavelength conversion element for emitting the fluorescence YL
toward the incident side of the blue light L1s. It should be noted
that the fluorescence YL is, for example, light having a peak
wavelength in a range of 500 nm through 700 nm. In other words, the
fluorescence YL includes a green light component and a red light
component.
The configuration of such a wavelength conversion element 51 will
be described later in detail.
The fluorescence YL having been emitted from the wavelength
conversion device 5 passes through the first light collection
element 46 along the illumination light axis Ax2, and then enters
the polarization split element 45. Then, the fluorescence YL passes
through the polarization split element 45 along the illumination
light axis Ax2.
Configuration of Second Retardation Element
The second retardation element 47 is disposed between the
polarization split element 45 and the second light collection
element 48. The second retardation element 47 is a 1/4 wave plate,
and the blue light L2p as the p-polarized light having passed
through the polarization split element 45 is converted by the
second retardation element 47 into blue light L2c as circularly
polarized light, and then enters the second light collection
element 48.
Configuration of Second Light Collection Element
The second light collection element 48 converges the blue light L2c
entering the second light collection element 48 from the first
retardation element 47 on the diffusely reflecting device 49.
Further, the second light collection element 48 collimates the blue
light L2c entering the second light collection element 48 from the
diffusely reflecting device 49. It should be noted that the number
of lenses constituting the second light collection element 48 can
arbitrarily be changed.
Configuration of Diffusely Reflecting Device
The diffusely reflecting device 49 diffusely reflects the blue
light L2c having entered the diffusely reflecting device 49 from
the second light collection element 48 toward the polarization
split element 45 at substantially the same diffusion angle as that
of the fluorescence YL emitted from the wavelength conversion
device 5. As a configuration of the diffusely reflecting device 49,
there can be illustrated a configuration provided with a reflecting
plate for performing Lambertian reflection on the blue light L2c
having entered the reflecting plate, and a rotation device for
rotating the reflecting plate around a rotational axis parallel to
the illumination light axis Ax1. In the light source device 4, by
diffusely reflecting the blue light L2c using this kind of
diffusely reflecting device 49, it is possible to obtain blue light
having a substantially uniform illuminance distribution.
As shown in FIG. 2, the blue light L2c having diffusely been
reflected by the diffusely reflecting device 49 passes through the
second light collection element 48, and then enters the second
retardation element 47 once again. The blue light L2c is converted
into circularly polarized light with the opposite rotational
direction when reflected by the diffusely reflecting device 49.
Therefore, the blue light L2c entering the second retardation
element 47 from the second light collection element 48 is converted
by the second retardation element 47 not into the blue light L2p as
the p-polarized light which enters the second retardation element
47 from the polarization split element 45, but into the blue light
L2s as the s-polarized light. Then, the blue light L2s as the
s-polarized light is reflected by the polarization split element
45, and then enters the homogenizing device 31 described above
along the illumination light axis Ax2 together with the
fluorescence YL.
Configuration of Wavelength Conversion Element
FIG. 3 is a plan view of the wavelength conversion element 51
viewed from the incident side of the excitation light. FIG. 4 is a
diagram schematically showing a cross-sectional surface of the
wavelength conversion element 51.
The wavelength conversion element 51 is a reflective wavelength
conversion element for emitting the fluorescence as the light
having a different wavelength from the wavelength of the excitation
light toward the incident side of the excitation light. As shown in
FIG. 3 and FIG. 4, the wavelength conversion element 51 has a
substrate 52, a radiator sheet 53, a phosphor layer 54, and an
antireflection layer 55. It should be noted that the wavelength
conversion element 51 is manufactured using a manufacturing method
described later.
It should be noted that in the following description and the
drawings, the blue light L1s entering the wavelength conversion
element 51 is described as excitation light for exciting the
phosphor particles included in the wavelength conversion element
51. Further, the incident direction of the excitation light to the
wavelength conversion element 51 is defined as a +Z direction, and
an opposite direction to the +Z direction is defined as a -Z
direction.
Configuration of Substrate
The substrate 52 is a holding member for holding the radiator sheet
53, the phosphor layer 54, and the antireflection layer 55, and in
addition, the substrate 52 is also a radiator member for radiating
the heat transferred from the phosphor layer 54. As shown in FIG.
3, the substrate 52 is formed of, for example, a metal material
including at least either of alumina and zinc oxide so as to have a
disk-like shape when viewed from the -Z direction. The substrate 52
is rotated together with the radiator sheet 53, the phosphor layer
54, and the antireflection layer 55 around the rotational axis Rx
by the rotary section RT.
As shown in FIG. 4, the substrate 52 has a first surface 521 as a
surface on the -Z direction side, and a second surface 522 as a
surface on the +Z direction side.
The first surface 521 is an opposed surface opposed to the phosphor
layer 54.
The second surface 522 is a surface on the opposite side to the
first surface 521. To the second surface 522, there is bonded the
radiator sheet 53, the heat generated in the phosphor layer 54 is
transferred to the radiator sheet 53 via the substrate 52, and heat
having been transferred is transferred to the entire area of the
radiator sheet 53. The radiator sheet 53 increases the contact area
with the ambient gas to thereby enhance the radiation efficiency of
the heat having been transferred to the substrate 52. The radiator
sheet 53 is formed of, for example, aluminum or graphite.
The substrate 52 is a sintered body obtained by calcining alumina
powder having a submicron size at low temperature to include
microscopic gas pockets as much as about 20% in volume, and
reflects the light entering the substrate 52 from the phosphor
layer 54 toward the phosphor layer 54 side.
Configuration of Phosphor Layer
The phosphor layer 54 is disposed on the -Z direction side as the
incident side of the excitation light with respect to the substrate
52. The phosphor layer 54 converts the excitation light entering
the phosphor layer 54 into fluorescence, and then emits the
fluorescence. In other words, the phosphor layer 54 performs the
wavelength conversion on the excitation light entering the phosphor
layer 54 to generate and then emit the fluorescence as the light
having a longer wavelength than the wavelength of the excitation
light. As shown in FIG. 3, the phosphor layer 54 is formed to have
an annular shape centered on the rotational axis Rx of the
wavelength conversion element 51 when viewed from the -Z
direction.
As shown in FIG. 4, the phosphor layer 54 has a first surface 541
as a surface on the -Z direction side, and a second surface 542 as
a surface on the +Z direction side, and a surface on an opposite
side to the first surface 541.
The first surface 541 is a plane of incidence which the excitation
light enters, and is an exit surface from which the fluorescence is
emitted. The second surface 542 is an opposed surface opposed to
the substrate 52.
FIG. 5 is a schematic diagram showing a part of the phosphor layer
54 and a part of the antireflection layer 55 in an enlarged manner.
In other words, FIG. 5 is a cross-sectional view schematically
showing a plurality of phosphor particles PR and a binder BN
constituting the phosphor layer 54 and the antireflection layer
55.
As shown in FIG. 5, the phosphor layer 54 includes the plurality of
phosphor particles PR and the binder BN including glass, and has a
configuration in which the phosphor particles PR are bound to each
other with the binder BN. Specifically, the two phosphor particles
PR adjacent to each other are bound to each other by the binder BN
to be bonded to a part of the surface of each of the phosphor
particles PR.
The phosphor particles PR are each a particle including a phosphor
material and an activator agent to be the light emission center. As
the activator agent, there can be cited, for example, Ce, Eu, Pr,
Cr, Gd, and Ga. As the phosphor material, there can be adopted a
YAG phosphor material. However, this is not a limitation, and as
the phosphor material, it is possible to adopt a phosphor material
obtained by displacing Y in the YAG phosphor with Lu, Gd, or GA, or
it is also possible to adopt a KSF phosphor material, an SCASN
phosphor material, or the like instead of the YAG phosphor
material. Further, the phosphor material can also be a mixture of a
plurality of phosphor materials.
The binder BN is bonded to a part of the surface of each of the
phosphor particles PR adjacent to each other out of the plurality
of phosphor particles PR to bind the phosphor particles PR adjacent
to each other. As the binder BN, there is used borosilicate glass
in the present embodiment, but phosphate glass can also be
used.
It should be noted that microscopic voids SP are disposed inside
the phosphor layer 54. Since such voids SP are included, spread of
the fluorescence inside the phosphor layer 54 is suppressed, and by
taking out the fluorescence from the phosphor layer 54 in a small
range, the light collection efficiency of the optical system can be
enhanced.
As shown in FIG. 4, the antireflection layer 55 is disposed on at
least the first surface 541 as the plane of incidence which the
excitation light enters in the phosphor layer 54, and is formed of
a single layer or a multilayered dielectric film. In other words,
the antireflection layer 55 is disposed on the incident side of the
excitation light with respect to the phosphor layer 54. The
antireflection layer 55 prevents the excitation light entering the
wavelength conversion element 51 from being reflected by the first
surface 541 to thereby make the excitation light easy to enter the
phosphor layer 54.
Such an antireflection layer 55 is formed on the phosphor layer 54
using vapor deposition or the like. Therefore, as shown in FIG. 5,
the antireflection layer 55 is formed so as to cover the plurality
of phosphor particles PRA located on the -Z direction side in the
phosphor layer 54 to form the first surface 541 out of the
plurality of phosphor particles PR, and the binder BN for binding
the plurality of phosphor particles PRA on the -Z direction
side.
In the present embodiment, the antireflection layer 55 is formed
only on the first surface 541 of the phosphor layer 54. However,
this is not a limitation, and the antireflection layer 55 can also
be formed on at least either of, for example, an inner peripheral
surface and an outer peripheral surface of the phosphor layer 54 in
addition to the first surface 541.
Relationship Between Area of Binding Part in Phosphor Particle and
Brightness in Optical System
FIG. 6 is a schematic diagram showing a binding state of the
phosphor particles PR with the binder BN. In other words, FIG. 6 is
a schematic diagram showing the state in which the phosphor
particles PR (PR1, PR2) adjacent to each other are bound to each
other with the binder BN.
As shown in FIG. 6, defining the region to which the binder BN is
bonded in the phosphor particle PR as a binding part B1, in the
present embodiment, the area of the binding part B1 is set to a
value no higher than 10% of the surface area of the phosphor
particle PR in order to increase the luminance of the light
transmitted through the optical device 30 as the optical system
which the illumination light including the fluorescence emitted
from the phosphor layer 54 enters. In the detailed description, the
area of the binding part B1 is set to a value within a range no
lower than 3% and no higher than 5% of the surface area of the
phosphor particle PR. This derives from the following experimental
result.
FIG. 7 is a graph showing the brightness in the optical system in
the optical device 30 and the spread of the light with respect to
the proportion of the area of the binding part B1 to the surface
area of the phosphor particle PR.
The inventors conducted an experiment of measuring the spread of
the light emitted from the phosphor layer 54 and the brightness in
the optical system in the optical device 30 while changing the
proportion of the area of the binding part B1 to the surface area
of the phosphor particle PR. It should be noted that the brightness
in the optical system mentioned here represents the intensity of
the light which can be converged on the light modulation devices
343. Further, the spread of the light is a proportion of the area
of the exit region of the fluorescence to the area of the incident
region of the excitation light in the first surface 541 of the
phosphor layer 54. In the following description, the proportion of
the area of the binding part B1 to the surface area of the phosphor
particle PR is abbreviated as an area proportion.
The higher the area proportion was, the broader the spread of the
light emitted from the phosphor layer 54 became as represented by
the dashed-dotted line in FIG. 7. In other words, the larger the
area of the binding part B1 was, the broader the spread of the
light emitted from the phosphor layer 54 became.
As represented by the solid line in FIG. 7, it was found out that
it was not true that the lower the area proportion was the higher
the brightness in the optical system became, but there existed the
maximum value (the highest value) in the brightness in the optical
system.
In the detailed description, in the range in which the area
proportion was no higher than 10%, the brightness in the optical
system increased and then decreased as the area proportion
increased. Further, it was found out that the maximum value of the
brightness in the optical system appeared when the area proportion
was in the range of no lower than 3% and no higher than 5%.
In contrast, in a range in which the area proportion exceeded 10%,
the brightness in the optical system was lower than the value when
the area proportion was 0%, and the higher the area proportion was,
the lower the brightness in the optical system became.
In other words, it was found out that the brightness in the optical
system became higher when the area proportion was no higher than
10% than the value when the area proportion was 0%, and took the
maximum value when the area proportion was in the range of no lower
than 3% and no higher than 5%.
It is conceivable that the reason that there exists the range of
the area proportion in which the brightness in the optical system
takes the high value as described above is as follows.
The refractive index of the phosphor particles PR is about 1.8. In
contrast, the refractive index of the borosilicate glass
constituting the binder BN is about 1.5.
Therefore, the fluorescence having been generated inside the
phosphor particle PR and then entered the binding part B1
propagates the binder BN from the binding part B1 to proceed to the
inside of the adjacent phosphor particles PR.
In contrast, since the voids SP are disposed inside the phosphor
layer 54, other areas than the binding part B1 have contact with
air on the outside surface of each of the phosphor particles PR.
Therefore, in accordance with the Fresnel formula, the fluorescence
which is generated inside the phosphor particle PR and then enters
the other areas than the binding part B1 in the outside surface of
the phosphor particle PR is mostly emitted outside the phosphor
particle PR and partially reflected inside the phosphor particle
PR, or is totally reflected inside the phosphor particle PR.
When the area proportion is high, the amount of fluorescence
entering the binding part B1 increases. In other words, when the
area proportion is high, the amount of fluorescence propagating the
binder BN via the binding part B1 increases. In this case, since a
difference between the refractive index of the phosphor particles
PR and the refractive index of the binder BN is small, and the
refraction on the interface between the phosphor particle PR and
the binder BN is small, the fluorescence becomes apt to spread to
the neighboring phosphor particles PR. Therefore, the fluorescence
goes out from the first surface 541 of the phosphor layer 54 to the
outside as a light source broad in spread. Thus, the fluorescence
having been emitted from the phosphor layer 54 becomes difficult to
be converged on the light modulation devices 343 of the optical
device 30 as the optical system. In other words, in this case, the
brightness in the optical system lowers.
When the area proportion is low, the fluorescence generated inside
the phosphor particle PR becomes easy to enter the other areas than
the binding part B1 on the outside surface of the phosphor particle
PR, namely the interface with the air. Therefore, since the
intensity of the fluorescence refracted on the interface between
the phosphor particle PR and the air, and emitted from the phosphor
particle PR, and the intensity of the fluorescence totally
reflected increase, the fluorescence is prevented from spreading to
the phosphor particles PR in a neighboring broad range, and the
fluorescence goes out as the light source small in spread to the
outside from the first surface 541 of the phosphor layer 54. Such
fluorescence is apt to converge on the light modulation devices
343. In other words, in this case, the brightness in the optical
system rises.
In contrast, when the area proportion has such an extremely small
value as, for example, a value no higher than 1%, the fluorescence
becomes apt to be confined inside the phosphor particle PR. In this
case, the reflection of the fluorescence on the interface with the
voids SP becomes apt to be repeated, and thus, the light path
length of the fluorescence increases. As described above, by the
fluorescence passing through the phosphor particle PR many times,
self-absorption becomes apt to occur. The self-absorption is a
phenomenon that the phosphor absorbs the fluorescence to generate
heat since the emission wavelength of the phosphor partially
overlaps the absorption wavelength of the phosphor. When such
self-absorption occurs, the intensity of the fluorescence emitted
from the phosphor layer 54 decreases, and by extension, the
brightness in the optical system decreases.
On the other hand, when the frequency of the reflection and the
refraction on the interface with the air in the phosphor particle
PR increases, the excitation light with which the phosphor
particles PR are irradiated from the outside of the phosphor layer
54 becomes apt to be reflected by the surface of each of the
phosphor particles PR, or the inside of each of the phosphor
particles PR. The intensity of the excitation light which is
radiated outside the phosphor layer 54 without being converted into
the fluorescence increases. In other words, backward scattering
(backscatter) of the excitation light becomes apt to occur. In this
case, by the intensity of the excitation light to be converted into
the fluorescence decreasing, the intensity of the fluorescence
emitted from the phosphor layer 54 decreases, and by extension, the
brightness in the optical system can decrease.
According to such a consideration, it has been understood that in
order to increase the brightness in the optical system, the area
proportion preferably has a value no higher than 10%, and more
preferably has a value no lower than 3% and no higher than 5%.
Size of Binding Part to Binder in Phosphor Particle
In the present embodiment, in order to make the proportion of the
area of the binding part B1 to the surface area of the phosphor
particle PR no higher than 10%, the phosphor layer 54 is
manufactured so that the size of the binding part B1 becomes the
following size. It should be noted that in the following
description, the phosphor particles bound to each other with the
binder BN and adjacent to each other out of the plurality of
phosphor particles PR are defined as the phosphor particles PR1,
PR2 as shown in FIG. 6. Further, the binding part B1 with the
binder BN in the phosphor particle PR1 is defined as the binding
part B11, and the binding part B1 with the binder BN in the
phosphor particle PR2 is defined as the binding part B12. Further,
the two axes which are perpendicular to an imaginary line VL
connecting the centers C1, C2 of the respective phosphor particles
PR1, PR2, and are perpendicular to each other are defined as an X
axis and a Y axis.
In the present embodiment, the dimension in the Y axis of the
binding part B11 is made no larger than 1/4 of the diameter D11 of
the phosphor particle PR1, and although not shown in the drawing,
the dimension in the X axis of the binding part B11 is made no
larger than 1/4 of the diameter D11 of the phosphor particle PR1.
In other words, the dimension in the Y axis of the binding part B11
is made no larger than 1/4 of the size in the Y axis of the
phosphor particle PR1, and although not shown in the drawing, the
dimension in the X axis of the binding part B11 is made no larger
than 1/4 of the size in the X axis of the phosphor particle
PR1.
Similarly, the dimension in the Y axis of the binding part B12 is
made no larger than 1/4 of the diameter D12 of the phosphor
particle PR2, and although not shown in the drawing, the dimension
in the X axis of the binding part B12 is made no larger than 1/4 of
the diameter D12 of the phosphor particle PR2. In other words, the
dimension in the Y axis of the binding part B12 is made no larger
than 2/4 of the size in the Y axis of the phosphor particle PR2,
and although not shown in the drawing, the dimension in the X axis
of the binding part B12 is made no larger than 1/4 of the size in
the X axis of the phosphor particle PR2.
Further, the thickness of the binder BN, namely the dimension of
the binder BN along the imaginary line VL is made no larger than
1/10 of the diameter of the phosphor particle PR.
As described above, since the dimension of the binding part B1 is
the size described above, the proportion described above becomes
the value no higher than 10%, and it is possible to increase the
brightness in the optical system.
Calculational Size of Binding Part
The area proportion described above for increasing the brightness
in the optical system is also supported by a calculation result
based on the diameter of the phosphor particle PR.
When the phosphor particles PR included in the phosphor layer 54
are each assumed to have a spherical shape, the surface area of the
phosphor particle PR with a radius of R is 4.pi.R.sup.2.
In contrast, when the phosphor particles PR each having a spherical
shape and uniformed in particle diameter are densely arranged, the
filling rate of the phosphor particles PR per unit volume is
typically 60 through 75%. In this case, the number of other
phosphor particles PR having contact with one phosphor particle PR
is 8 through 12.
When the number of the other phosphor particles PR having contact
with the one phosphor particle PR is assumed as 8, and the binder
BN is assumed as a circular cylinder having a thickness of t and a
radius of r, the total area of the binding part B1 is 8.pi.r.sup.2.
It should be noted that the thickness of the binder BN is a
dimension along the imaginary line VL shown in FIG. 6.
According to the above, the area proportion described above is
obtained as 8.pi.r.sup.2/(4.pi.R.sup.2). In other words, the area
proportion described above becomes 2r.sup.2/R.sup.2.
When assuming the radius R of the phosphor particle PR as 12 .mu.m,
and assuming the proportion of the binding part B1 to the surface
area of the phosphor particle PR as 5% (=0.05) based on the
experimental result described above, the radius r of the binding
part B1 becomes about 1.89 .mu.m. In other words, the radius r of
the binding part B1 when using a circle as the shape of the binding
part B1 in the phosphor particle PR becomes about 2 .mu.m, and the
diameter of the binding part B1 becomes about 4 .mu.m. Further,
assuming the number of the other phosphor particles PR having
contact with the one phosphor particle PR as 12, the radius r of
the binding part B1 becomes about 3 .mu.m, and the diameter of the
binding part B1 becomes about 6 .mu.m. Therefore, the radius r of
the binding part B1 is about 2 through 3 .mu.m, and the diameter of
the binding part B1 is about 4 through 6 .mu.m.
The diameter of the binding part B1 obtained by such calculation is
a value no larger than 1/4 of the diameter 24 .mu.m of the phosphor
particle PR based on the assumption described above. In other
words, the dimensions in the X axis and the Y axis of the binding
part B1 are each a value no larger than 1/4 of the diameter of the
phosphor particle PR.
As described hereinabove, by setting the dimension of the binding
part B1 to the size described above with respect to the diameter of
the phosphor particle PR, it is possible to make the area
proportion described above no higher than 10%, and by extension, it
is possible to increase the brightness in the optical system.
The size of such a binding part B1 can be achieved by adjusting the
temperature when manufacturing the phosphor layer 54 although
described later in detail. This point will be described in a method
of manufacturing the wavelength conversion element 51.
Glass Content Rate in Phosphor Layer
FIG. 8 is a graph showing a relationship between a glass content
rate of the phosphor layer 54 and optical system efficiency.
It should be noted that the glass content rate is represented by
volume percent (vol %) of the binder BN in the phosphor layer 54.
Specifically, the glass content rate is "100*(volume of
glass)/((volume of glass)+(volume of phosphor particles))," and the
volume of the voids SP is not included.
In other words, the glass content rate mentioned here is not a
measured value of the wavelength conversion element 51 after being
manufactured, but is a value based on the volume percent of the
input of the binder BN and the phosphor particles PR in a paste
preparation step S1 and a phosphor mixing step S2 (see FIG. 14) in
the process of manufacturing the wavelength conversion element 51
described later.
In contrast, the optical system efficiency is "(the intensity of
the light having been emitted from the phosphor layer 54,
transmitted through the optical device 30 as the optical system,
and then emitted from the projection optical device 36)/(the
intensity of the excitation light with which the phosphor layer 54
has been irradiated)." Therefore, the optical system efficiency is
neither "(the intensity of the light having been emitted from the
phosphor layer 54 and then entered the optical device 30)/(the
intensity of the excitation light with which the phosphor layer 54
has been irradiated)" nor the wavelength conversion efficiency
expressed by "(the intensity of the light having been emitted from
the phosphor layer 54)/(the intensity of the excitation light with
which the phosphor layer 54 has been irradiated)."
In other words, the optical system efficiency is the efficiency
including etendue, and can be rephrased as the light use efficiency
in the optical device 30 of the projector 1.
As shown in FIG. 8, in the phosphor layer 54 related to the present
embodiment, in a range in which the glass content rate is higher
than 0 vol % and no higher than 10 vol %, the optical system
efficiency is made higher compared to when the glass content rate
is 0 vol %. Further, when the glass content rate is 10 vol %, the
optical system efficiency takes substantially the same value as
when the glass content rate is 0 vol %.
When the glass content rate exceeds 10 vol %, the optical system
efficiency lowers compared to when the glass content rate is 0 vol
%. It is conceivable that this is because the fluorescence spreads
in the phosphor layer 54 while the loss caused by the fluorescence
being reflected and refracted on the interface between the phosphor
particle PR and the binder BN decreases as described above, the
spread of the light when the fluorescence is emitted from the
phosphor layer 54 increases, and the intensity of the light which
can be used in the optical device 30 as the optical system
decreases to appear as a difference in measurement value. Further,
it is conceivable that the reason that the peak is shown in a range
of 0 through 10% is that when the binder BN is extremely small in
amount, the excitation light repeats the reflection and the
refraction a number of times on the interface between the phosphor
particle PR and the void SP (air), and thus, the excitation light
is discharged from the phosphor layer 54 before exciting the
phosphor.
FIG. 9 shows an image obtained when observing the phosphor layer
the glass content rate of which is 30 vol %, and which is formed at
calcination temperature of 1000.degree. C. with an SEM (Scanning
Electron Microscope). The image observed by the SEM is hereinafter
abbreviated as an SEM image.
FIG. 10 shows an SEM image of the phosphor layer the glass content
rate of which is 20 vol %, and which is formed at the calcination
temperature of 1000.degree. C. FIG. 11 shows an SEM image of the
phosphor layer the glass content rate of which is 10 vol %, and
which is formed at the calcination temperature of 1000.degree. C.
FIG. 12 shows an SEM image of the phosphor layer the glass content
rate of which is 5 vol %, and which is formed at the calcination
temperature of 1000.degree. C. FIG. 13 shows an SEM image of the
phosphor layer the glass content rate of which is 3 vol %, and
which is formed at the calcination temperature of 1000.degree.
C.
In the phosphor layer the glass content rate of which is 30 vol %,
and the phosphor layer the glass content rate of which is 20 vol %,
the surface of all of the phosphor particles PR is substantially
completely covered with the binder BN as shown in FIG. 9 and FIG.
10. In particular, in the phosphor layer the glass content rate of
which is 30 vol % shown in FIG. 9, the phosphor particles PR are
buried in the binder BN. When the phosphor particles PR are covered
with the binder BN as borosilicate glass in such a manner, the
fluorescence generated in the phosphor particles PR becomes easy to
propagate the binder BN, the spread of the light emitted from the
phosphor layer broadens, and the optical system efficiency
decreases as described above.
In contrast, in the phosphor layers the glass content rates of
which are 10 vol %, 5 vol %, and 3 vol %, respectively, the binder
BN is disposed between the phosphor particles PR adjacent to each
other, and the phosphor particles PR are not completely covered
with the binder BN as shown in FIG. 11 through FIG. 13. In
particular, in the phosphor layers the glass content rates of which
are 5 vol % and 3 vol %, respectively, the binder BN is only
disposed between the phosphor particles PR adjacent to each other,
and the surface of each of the phosphor particles PR is almost
exposed as shown in FIG. 12 and FIG. 13.
As described above, since the phosphor particles PR adjacent to
each other are bound to each other in a part of the surface with
the binder BN, and the other part is exposed, the spread of the
light emitted from the phosphor layer decreases, and thus, the
optical system efficiency is enhanced.
Therefore, by setting the glass content rate to the value within
the range higher than 0 vol % and no higher than 10 vol %, it is
possible to constitute the phosphor layer capable of increasing the
optical system efficiency compared to when the glass content rate
is 0 vol %, and when the glass content rate is higher than 10 vol
%.
Method of Manufacturing Wavelength Conversion Element
FIG. 14 is a flowchart showing the method of manufacturing the
wavelength conversion element 51.
The method of manufacturing the wavelength conversion element 51
including the phosphor layer 54 described above will be
described.
As shown in FIG. 14, the method of manufacturing the wavelength
conversion element 51 includes the paste preparation step S1, the
phosphor mixing step S2, a printing plate forming step S3, a
coating step S4, a drying step S5, a calcination step S6, a cooling
step S7, and a layer forming step S8 to be executed in sequence. In
other words, the method of manufacturing the wavelength conversion
element 51 described hereinafter includes the manufacturing method
according to the present disclosure.
The paste preparation step S1 and the phosphor mixing step S2
correspond to a preparation step.
The paste preparation step S1 is a step of mixing a binder
constituent to form the binder BN after the calcination, resin such
as ethyl cellulose, and a solvent for solving the binder
constituent and the resin with each other to prepare a glass paste.
It should be noted that the resin is for providing the paste with
viscosity. Further, as the binder constituent, there can be cited
what is obtained by fracturing the borosilicate glass including,
for example, silica as much as 60% or more into particles having a
diameter no larger than 1 .mu.m.
The phosphor mixing step S2 is a step of preparing a mixture paste
obtained by mixing the phosphor particles PR in the glass paste
thus prepared. The ratio between the phosphor particles PR and the
borosilicate glass as the binder constituent is set to a ratio
within a range of 98:2 through 92:8 in the volume ratio. It should
be noted that the range includes 98:2 and 92:8. More preferably,
the ratio between the phosphor particles PR and the borosilicate
glass is set to a ratio within a range of 97:3 through 95:5 in the
volume ratio. The range includes 97:3 and 95:5. By adjusting the
ratio between the phosphor particles PR and the borosilicate glass
as described above, it is possible to set the glass content rate to
a value within the range described above.
In the printing plate forming step S3, the printing plate is
manufactured so that printing drops out in a circular shape.
In the coating step S4, the mixture paste prepared in the phosphor
mixing step S2 is applied by printing with a thickness of 80 .mu.m
on a reflecting plate having a disk-like shape using the printing
plate thus manufactured. The reflecting plate is the substrate 52
provided with the microscopic gas pockets for reflection disposed
inside.
In the drying step S5, the mixture paste applied thereon is dried
for a short time at around 100.degree. C.
In the calcination step S6, the mixture paste thus dried is
calcined for a short time while raising the temperature at the
ratio of 10.degree. C./minute up to 1000.degree. C. by a firing
furnace. When calcining the mixture paste in the calcination step
S6, almost the whole of the resin and the solvent included in the
mixture paste evaporates. It should be noted that the calcination
temperature in the calcination step S6 will be described later in
detail.
In the cooling step S7, the mixture paste thus calcined is
cooled.
In the layer forming step S8, the antireflection layer 55 is formed
on the phosphor layer 54 as the mixture paste thus cooled in the
cooling step S7. Specifically, in the layer forming step S8, a
dielectric film is formed on the first surface 541 which is a
surface on an opposite side to the substrate 52 in the phosphor
layer 54 and which the excitation light enters using vapor
deposition or the like to thereby form the antireflection layer 55
on the first surface 541. Alternatively, as a method of attaching a
layer on a curved surface located in an upper part of the phosphor
layer 54 and an internal surface of the phosphor layer 54, it is
possible to use CVD (Chemical Vapor Deposition) or ALD (Atomic
Layer Deposition). Thus, it is possible to deliver a gas such as
SiO.sub.2 or TiO.sub.2 as a dielectric substance into every corner
of the inside of the phosphor layer 54 to deposit the film. Thus,
the excitation light is prevented from being reflected by the
surface of the phosphor particle PR even when the excitation light
reaches the inside of the phosphor layer 54, and thus, it is
possible to convert a larger amount of excitation light into the
fluorescence.
Due to the manufacturing method including the steps S1 through S8
described hereinabove, there is manufactured the wavelength
conversion element 51 having the phosphor layer 54 the area
proportion and the glass content rate of which are higher than 0%
and no higher than 10%.
Relationship Between Calcination Temperature and Viscosity of Glass
in Calcination Process
FIG. 15 is a graph showing a relationship between the calcination
temperature and the viscosity of the glass.
As shown in FIG. 15, the viscosity of the glass decreases as the
temperature rises, and the force due to the viscosity of the glass
weakens as the viscosity decreases. Further, assuming that the
softening point as a temperature at which the glass starts to
conspicuously soften to deform under its own weight, and at which
the viscosity becomes about 10.sup.70.6 dPas is 700.degree. C., by
making the calcination temperature in the calcination step S6
described above no lower than 800.degree. C. which is 100.degree.
C. higher than the softening point, the viscosity of the glass
becomes no higher than 10.sup.6 dPas (=10.sup.6 P).
Hereinafter, there is shown an SEM image of the phosphor layer
manufactured by calcining the mixture paste having the glass
content rate of 5 vol % at the calcination temperature.
In other words, FIG. 16 shows an SEM image showing a phosphor layer
the glass content rate of which is 5 vol %, and which is
manufactured by being calcined at 750.degree. C. FIG. 17 shows an
SEM image showing a phosphor layer the glass content rate of which
is 5 vol %, and which is manufactured by being calcined at
800.degree. C. FIG. 18 shows an SEM image showing a phosphor layer
the glass content rate of which is 5 vol %, and which is
manufactured by being calcined at 850.degree. C. FIG. 19 shows an
SEM image showing a phosphor layer the glass content rate of which
is 5 vol %, and which is manufactured by being calcined at
900.degree. C. FIG. 20 shows an SEM image showing a phosphor layer
the glass content rate of which is 5 vol %, and which is
manufactured by being calcined at 950.degree. C.
It should be noted that FIG. 12 shows the SEM image of the phosphor
layer the glass content rate of which is 5 vol %, and which is
manufactured by being calcined at 1000.degree. C. as described
above.
In the phosphor layer calcined at 750.degree. C. close to the
softening point of the glass, the size of the binding part B1 with
respect to the diameter of the phosphor particle PR is
substantially the same as described above as shown in FIG. 16. In
other words, the size of the binding part B1 with respect to the
diameter of the phosphor particle PR is no larger than 1/4 of the
diameter of the phosphor particle PR. However, since the binder BN
has a granular form, and in addition, the surface is not smooth,
the fluorescence and the excitation light having entered the binder
BN are apt to be scattered. When the scattering of the fluorescence
and the excitation light increases, the light path length of the
fluorescence increases, and when the light path length of the
fluorescence increases, the intensity of the fluorescence decreases
since the frequency of occurrence of the self-absorption by the
phosphor particles PR increases, and the excitation light is
reflected to the outside of the phosphor layer 54 without exciting
the phosphor particles PR as described above. Therefore, in the
phosphor layer calcined at 750.degree. C., the intensity of the
fluorescence emitted from the phosphor layer decreases, and the
optical system efficiency described above is apt to decrease.
In contrast, in the phosphor layer calcined at 800.degree. C., the
size of the binding part B1 with respect to the diameter of the
phosphor particle PR is substantially the same as described above
as shown in FIG. 17. In other words, the size of the binding part
B1 with respect to the diameter of the phosphor particle PR is no
larger than 1/4 of the diameter of the phosphor particle PR.
However, the size of the binding part B1 in the phosphor layer
calcined at 800.degree. C. becomes smaller than the size of the
binding part B1 in the phosphor layer calcined at 750.degree. C.
Besides the above, since the calcination temperature is 100.degree.
C. higher than the softening point, and the viscosity is
sufficiently low, the surface of the binder BN is made smooth, and
the fluorescence having entered the binder BN is difficult to
scatter. Further, as shown in FIG. 17, when the calcination
temperature is 800.degree. C., the viscosity of the glass becomes
no higher than 10.sup.6 dPas (=10.sup.6 P), and since the viscosity
is sufficiently low, the surface of the binder BN is made smooth,
and thus, the fluorescence having entered the binder BN is
difficult to scatter. Therefore, the occurrence of the
self-absorption by the phosphor particles PR is suppressed, and the
intensity of the fluorescence is prevented from decreasing compared
to the phosphor layer calcined at 750.degree. C.
Substantially the same as above also applies to the phosphor layers
calcined at 850.degree. C., 900.degree. C., and 950.degree. C.
shown in FIG. 18 through FIG. 20, respectively, and the phosphor
layer calcined at 1000.degree. C. shown in FIG. 12. In other words,
since the viscosity of the glass decreases as the calcination
temperature rises, the size of the binding part B1 decreases, and
in addition, the thickness of the binder BN as the dimension in the
direction connecting the phosphor particles PR to be bound also
decreases. Further, the surface of the binder BN in the phosphor
layer becomes smoother, and the scattering of the fluorescence is
further suppressed. It is conceivable that substantially the same
is applied to a phosphor layer calcined at a temperature exceeding
1000.degree. C.
In particular, when the calcination temperature becomes no higher
than 900.degree. C., the viscosity becomes no higher than 10.sup.5
dPas, the fluidity of the glass is enhanced, and the binder BN
becomes in a state which is desirable from an optical point of view
and a viewpoint of thermal conduction, and in which the binder BN
has a streamline shape to bond the phosphor particles PR adjacent
to each other. Further, it is understood from FIG. 12 that when the
calcination temperature becomes 1000.degree. C., the viscosity
becomes 10.sup.4 dPas, and there is achieved the bonding state with
near-complete fluidity.
On the other hand, when the calcination temperature in the
calcination step S6 described above is made no lower than
1100.degree. C., Ce ions as the activator agent of the phosphor are
oxidized to thereby be deactivated. Therefore, from a viewpoint of
the manufacturing process, it is more preferable for the
calcination temperature in the calcination step S6 to be no lower
than 800.degree. C. and no higher than 1100.degree. C. (100.degree.
C. or more and 400.degree. C. or less higher than the softening
point). Among the above, when the calcination temperature in the
calcination step S6 is no lower than 900.degree. C. and no higher
than 1100.degree. C. (200.degree. C. or more and 400.degree. C. or
less higher than the softening point), the viscosity no higher than
10.sup.5 dPas can preferably be realized. Further, it is more
desirable for the calcination temperature in the calcination step
S6 to be no lower than 950.degree. C. and no higher than
1050.degree. C. (250.degree. C. or more and 350.degree. C. or less
higher than the softening point). This is a temperature for
realizing the viscosity of 10.sup.4 dPas, the phosphor layer is
higher in emission efficiency, and the optical system efficiency
described above including the optical device 30 is high.
Advantages of First Embodiment
According to a process of manufacturing the projector 1 and the
wavelength conversion element 51 related to the present embodiment
described hereinabove, the following advantages can be exerted.
The projector 1 is provided with the light source device 4, the
light modulation devices 343 (343B, 343G, and 343R) for modulating
the light emitted from the light source device 4 in accordance with
the image information, and the projection optical device 36 for
projecting the light modulated by the light modulation devices 343.
The light source device 4 is provided with the light source 411 for
emitting the excitation light, and the wavelength conversion
element 51 for performing the wavelength conversion on the
excitation light to generate the fluorescence having a longer
wavelength than the wavelength of the excitation light. The
wavelength conversion element 51 is provided with the phosphor
layer 54 having the plurality of phosphor particles PR, and the
binder BN for binding one phosphor particle PR1 and the other
phosphor particle PR2 adjacent to each other out of the plurality
of phosphor particles PR, the antireflection layer 55 disposed on
the incident side of the excitation light with respect to the
phosphor layer 54, and the substrate 52 on which the phosphor layer
54 is disposed. The binder BN includes the glass, and the binder BN
binds a part of the surface of the one phosphor particle PR1 and a
part of the surface of the other phosphor particle PR2 to each
other.
According to such a configuration, the binder BN is not bonded to
the entire surface of each of the phosphor particles PR, but is
bonded to only a part of the surface in each of the phosphor
particles PR. This makes it possible to reduce the area of the
binding part B1 to be bonded to the binder BN in the surface of the
phosphor particle PR. In other words, it is possible to increase
the area of the region having contact with the void SP (air) in the
surface of the phosphor particle PR. Thus, since it is possible to
decrease the intensity of the fluorescence propagating the binder
BN, it is possible to decrease the spread of the light emitted from
the phosphor layer 54, and by extension, from the wavelength
conversion element 51. Therefore, it is possible to enhance the
brightness in the optical device 30 as the optical system, and
thus, it is possible to increase the optical system efficiency
described above.
Further, on the incident side of the excitation light with respect
to the phosphor layer 54, there is disposed the antireflection
layer 55. Specifically, on the first surface 541 as the plane of
incidence of the excitation light in the phosphor layer 54, there
is disposed the antireflection layer 55. According to this
configuration, it is possible to make the excitation light entering
the wavelength conversion element 51 easy to enter the phosphor
layer 54, and thus, it is possible to reduce the intensity of the
excitation light which is reflected by the first surface 541 and
fails to enter the phosphor layer 54. Therefore, it is possible to
enhance the wavelength conversion efficiency of the wavelength
conversion element 51, and thus, it is possible to increase the
intensity of the fluorescence to be emitted from the wavelength
conversion element 51 compared to the wavelength conversion element
51 which is not provided with the antireflection layer 55.
When manufacturing the phosphor layer 54, the proportion of the
volume of the binder BN to the total volume of the sum of the
volumes of the phosphor particles PR and the sum of the volumes of
the binder BN is larger than 0 vol % and no larger than 10 vol %.
In other words, the glass content rate in the mixture paste
prepared when manufacturing the phosphor layer 54 is larger than 0
vol % and no larger than 10 vol %.
According to such a configuration, as described above, it is
possible to reduce the area of the binding part B1 to be bonded to
the binder BN in the surface of the phosphor particle PR. Thus, it
is possible to decrease the intensity of the fluorescence
propagating inside the binder BN, and it is possible to decrease
the spread of the fluorescence emitted from the phosphor layer 54,
and by extension, from the wavelength conversion element 51.
Therefore, it is possible to enhance the brightness in the optical
device 30 as the optical system, and thus, it is possible to
increase the optical system efficiency described above.
The method of manufacturing the wavelength conversion element
includes the preparation step of preparing the mixture obtained by
mixing the phosphor particles and the binder including the glass
with each other, the coating step of applying the mixture on the
substrate, the calcination step of calcining the substrate coated
with the mixture, and the layer forming step of forming the
antireflection layer on the surface on the opposite side to the
substrate in the mixture thus calcined, and the calcination
temperature in the calcination step is 100.degree. C. or more
higher than the softening point of the glass. Specifically, the
method of manufacturing the wavelength conversion element 51
includes the paste preparation step S1 and the phosphor mixing step
S2 as the preparation step, the coating step S4, the calcination
step S6, and the layer forming step S8. In the paste preparation
step S1 and the phosphor mixing step S2, there is prepared the
mixture paste as the mixture obtained by mixing the phosphor
particles PR and the binder including the glass with each other. In
the coating step S4, the mixture paste is applied on the substrate
52. In the calcination step S6, the substrate 52 coated with the
mixture paste is calcined. In the layer forming step S8, the
antireflection layer 55 is formed on the first surface 541 on the
opposite side to the substrate 52 in the phosphor layer 54 as the
mixture paste thus calcined. Further, the calcination temperature
in the calcination step S6 is 100.degree. C. or more higher than
the softening point of the glass.
In other words, the method of manufacturing the wavelength
conversion element includes the preparation step of preparing the
mixture obtained by mixing the phosphor particles and the binder
including the glass with each other, the coating step of applying
the mixture on the substrate, the calcination step of calcining the
substrate coated with the mixture, and the layer forming step of
forming the antireflection layer on the surface on the opposite
side to the substrate in the mixture thus calcined, and the
viscosity of the glass in the calcination step is no higher than
10.sup.6 dPas. Specifically, the method of manufacturing the
wavelength conversion element 51 includes the paste preparation
step S1, the phosphor mixing step S2, the coating step S4, the
calcination step S6, and the layer forming step S8 described above,
and the viscosity of the glass in the calcination step S6 is no
higher than 10.sup.6 dPas.
Second Embodiment
Then, a second embodiment of the present disclosure will be
described.
The projector according to the present embodiment is provided with
substantially the same configuration as that of the projector 1
described in the first embodiment, but is different therefrom in
the configuration of the wavelength conversion element. It should
be noted that in the following description, a part which is the
same or substantially the same as the part having already been
described is denoted by the same reference symbol, and the
description thereof will be omitted.
FIG. 21 is a schematic diagram showing a cross-sectional surface of
a wavelength conversion element 51A provided to the projector
according to the present embodiment.
The projector according to the present embodiment has substantially
the same configuration and functions as those of the projector 1
except the point that the wavelength conversion element 51A is
provided instead of the wavelength conversion element 51. In other
words, in the present embodiment, the light source device 4 has the
wavelength conversion element 51A instead of the wavelength
conversion element 51.
As shown in FIG. 21, the wavelength conversion element 51A has
substantially the same configuration and functions as those of the
wavelength conversion element 51 except the point that the
wavelength conversion element 51A has a phosphor layer 56 instead
of the phosphor layer 54, but does not have the antireflection
layer 55. Specifically, the wavelength conversion element 51A has
the substrate 52, the radiator sheet 53, and the phosphor layer 56.
The wavelength conversion element 51A is manufactured using a
manufacturing method described later.
Configuration of Phosphor Layer
FIG. 22 is a schematic diagram showing the binding state of the
plurality of phosphor particles PR and the binder BN constituting
the phosphor layer 56. Further, FIG. 23 is a schematic diagram
showing a binding state of the phosphor particles PR adjacent to
each other with the binder BN.
Similarly to the phosphor layer 54, the phosphor layer 56 is
excited by the excitation light entering the phosphor layer 56 to
emit the fluorescence as the light different in wavelength from the
excitation light. The phosphor layer 56 is held by the substrate 52
located on the +Z direction side with respect to the phosphor layer
56.
The phosphor layer 56 has a first surface 561 as a surface on the
-Z direction side, and a second surface 562 as a surface on the +Z
direction side, and a surface on an opposite side to the first
surface 561.
The first surface 561 is a plane of incidence which the excitation
light enters, and is an exit surface from which the fluorescence is
emitted. The second surface 562 is an opposed surface opposed to
the first surface 521 of the substrate 52.
Such a phosphor layer 56 includes a plurality of particles PA, the
binder BN including glass, and the voids SP, and is constituted by
the plurality of particles PA bound to each other with the binder
BN.
The glass content rate in the phosphor layer 56 is a value within a
range no lower than 0 vol % and no higher than 10 vol % similarly
to the phosphor layer 54. It should be noted that the definition of
the glass content rate in the present embodiment is substantially
the same as described above.
Configuration of Particles
As shown in FIG. 22 and FIG. 23, the particles PA each have the
phosphor particle PR and an antireflection layer AR disposed on the
surface of the phosphor particle PR. In other words, the phosphor
layer 56 has the plurality of phosphor particles PR, the binder BN
for binding the phosphor particles PR adjacent to each other out of
the plurality of phosphor particles PR to each other, and the
antireflection layer AR disposed on the surface of each of the
phosphor particles PR.
The antireflection layer AR prevents the excitation light entering
the phosphor particle PR from being reflected by the surface of the
particle PA to thereby make the excitation light easy to enter the
phosphor particle PR. In the method of manufacturing the wavelength
conversion element 51 described later, the antireflection layer AR
is formed on the surface of each of the phosphor particles PR
before being mixed with the binder BN. Therefore, the
antireflection layer AR is formed on substantially the entire
surface of each of the phosphor particles PR. Such an
antireflection layer AR can be a single layer film made of, for
example, magnesium fluoride, or can also be a multilayered film
obtained by stacking titanium oxide and silicon oxide on one
another.
It should be noted that substantially the entire surface of the
phosphor particle PR on which the antireflection layer AR is formed
includes the entire surface of the phosphor particle PR. In other
words, providing the antireflection layer AR is formed in a range
which can be called substantially the entire surface on the surface
of the phosphor particle PR, the antireflection layer AR is not
necessarily required to be formed on the entire surface of the
particle PA.
As shown in FIG. 23, in the particle PA, the binder BN is bonded to
a part of the surface. In other words, the binder BN is bonded to a
part of the surface of the phosphor particle PR on which the
antireflection layer AR has been disposed. Specifically, the binder
BN is bonded to the antireflection layer AR in some cases, and in
other cases, the binder BN is bonded to the surface of the phosphor
particle PR.
Therefore, out of the phosphor particles PR adjacent to each other,
the binder BN binds at least any one of the pairs of the surface of
one phosphor particle PR (PR3) and the surface of the other
phosphor particle PR (PR4), the antireflection layer AR disposed on
the surface of the one phosphor particle PR (PR3) and the
antireflection layer AR disposed on the surface of the other
phosphor particle PR (PR4), and the surface of the one phosphor
particle PR (PR3) and the antireflection layer AR disposed on the
surface of the other phosphor particle PR (PR4).
In other words, the phosphor particles PR each have a binding part
B2 bound to another phosphor particle PR via the binder BN.
Further, in the surface of the phosphor particle PR, a region other
than the binding part B2 has contact with the void SP (air), or has
contact with the void SP (air) via the antireflection layer AR.
Here, out of the plurality of particles PA, the particles PA
adjacent to each other are defined as the particle PA1, PA2, the
phosphor particle PR constituting the particle PA1 is defined as
the phosphor particle PR3, and the phosphor particle PR
constituting the particle PA2 is defined as the phosphor particle
PR4. Further, the binding part B2 in the phosphor particle PR3 is
defined as the binding part B21, and the binding part B2 in the
phosphor particle PR4 is defined as the binding part B22.
In this case, the proportion of the area of the binding part B21 to
the surface area of the phosphor particle PR3 is no higher than
10%, and is specifically no lower than 3% and no higher than 5%
similarly to the area proportion in the first embodiment.
Similarly, the proportion of the area of the binding part B22 to
the surface area of the phosphor particle PR4 is also no higher
than 10%, and is specifically no lower than 3% and no higher than
5%.
Further, the dimension in the Y axis of the binding part B21 is no
larger than 1/4 of the diameter D21 of the phosphor particle PR3,
and although not shown in the drawing, the dimension in the X axis
of the binding part B21 is no larger than 1/4 of the diameter D21
of the phosphor particle PR3. In other words, the dimension in the
Y axis of the binding part B21 is no larger than 1/4 of the size in
the Y axis of the phosphor particle PR3, and although not shown in
the drawing, the dimension in the X axis of the binding part B21 is
no larger than 1/4 of the size in the X axis of the phosphor
particle PR3. Further, the dimension in the Y axis of the binding
part B22 is no larger than 1/4 of the diameter D22 of the phosphor
particle PR4, and although not shown in the drawing, the dimension
in the X axis of the binding part B22 is no larger than 1/4 of the
diameter D22 of the phosphor particle PR4. In other words, the
dimension in the Y axis of the binding part B22 is no larger than
1/4 of the size in the Y axis of the phosphor particle PR4, and
although not shown in the drawing, the dimension in the X axis of
the binding part B22 is no larger than 1/4 of the size in the X
axis of the phosphor particle PR4.
Further, the thickness of the binder BN, namely the dimension of
the binder BN in a direction connecting the center of the phosphor
particle PR3 and the center of the phosphor particle PR4 to each
other, is no larger than 1/10 of the diameter of the phosphor
particle PR.
Method of Manufacturing Wavelength Conversion Element
FIG. 24 is a flowchart showing the method of manufacturing the
wavelength conversion element 51A.
As shown in FIG. 24, the method of manufacturing the wavelength
conversion element 51A includes a layer forming step SA, the paste
preparation step S1, a phosphor mixing step S2A, the printing plate
forming step S3, the coating step S4, the drying step S5, the
calcination step S6, and the cooling step S7 to be executed in
sequence.
The layer forming step SA is a step of forming the antireflection
layer AR on each of the phosphor particles PR to prepare the
particles PA to be mixed with the binder constituent and so on in
the phosphor mixing step S2A. In other words, in the layer forming
step SA, there is formed the antireflection layer AR on the surface
of each of the phosphor particles PR. It should be noted that as a
method of forming the antireflection layer AR on the phosphor
particles PR, there can be cited ALD (Atomic Layer Deposition), and
a method of performing sputter-coating on the surface of each of
the phosphor particles PR with the antireflection layer AR using a
gas while rotating a polygonal barrel containing a powder.
The paste preparation step S1 and the phosphor mixing step S2A
correspond to the preparation step.
Out of these steps S1, S2A, in the phosphor mixing step S2A, the
glass paste prepared in the paste preparation step S1 and the
particles PA as the phosphor particles PR provided with the
antireflection layers AR in the layer forming step SA are mixed
with each other so that the ratio between the phosphor particles PR
and the binder constituent becomes the ratio described above.
The printing plate forming step S3, the coating step S4, the drying
step S5, the calcination step S6, and the cooling step S7 are
substantially the same as the steps S3 through S7, respectively, in
the method of manufacturing the wavelength conversion element 51
described above. Specifically, the calcination temperature in the
calcination step S6 is a temperature no lower than 800.degree. C.
as a temperature 100.degree. C. or more higher than the softening
point of the borosilicate glass as the binder constituent, and is
preferably no lower than 800.degree. C. and no higher than
1000.degree. C. Further, the viscosity of the borosilicate glass
when calcined at such a calcination temperature is no higher than
10.sup.6 dPas (=10.sup.6 P).
Due to the manufacturing method including the steps SA, and S1
through S7 described hereinabove, there is manufactured the
wavelength conversion element 51A having the phosphor layer 56 the
area proportion and the glass content rate of which are higher than
0% and no higher than 10%.
Advantages of Second Embodiment
According to the projector related to the present embodiment
described hereinabove, the advantages substantially the same as
those of the projector 1 described in the first embodiment can be
exerted.
Specifically, the projector according to the present embodiment is
provided with the light source device 4, the light modulation
devices 343 (343B, 343G, and 343R) for modulating the light emitted
from the light source device 4 in accordance with the image
information, and the projection optical device 36 for projecting
the light modulated by the light modulation devices 343. The light
source device 4 is provided with the light source 411 for emitting
the excitation light, and the wavelength conversion element 51A for
performing the wavelength conversion on the excitation light to
generate the fluorescence having a longer wavelength than the
wavelength of the excitation light. The wavelength conversion
element 51A is provided with the phosphor layer 56 having the
plurality of phosphor particles PR, and the binder BN for binding
one phosphor particle PR (PR3) and the other phosphor particle PR
(PR4) adjacent to each other out of the plurality of phosphor
particles PR, and the antireflection layer AR disposed on the
surface of each of the phosphor particles PR, and the substrate 52
on which the phosphor layer 56 is disposed. The binder BN includes
the glass. The binder BN binds at least any one of the pairs of a
part of the surface of one phosphor particle PR (PR3) and a part of
the surface of the other phosphor particle PR (PR4), the
antireflection layer AR disposed on the surface of the one phosphor
particle PR (PR3) and the antireflection layer AR disposed on the
surface of the other phosphor particle PR (PR4), and a part of the
surface of the one phosphor particle PR (PR3) and the
antireflection layer AR disposed on the surface of the other
phosphor particle PR (PR4).
According to such a configuration, the binder BN is not bonded to
the entire surface of each of the particles PA, namely the entire
surface of each of the phosphor particles PR, but is bonded to only
a part of the surface in each of the phosphor particles PR. This
makes it possible to reduce the area of the binding part B2 to be
bonded to the binder BN in the surface of the phosphor particle PR.
In other words, it is possible to increase the area of the region
having contact with the void SP (air) in the surface of the
phosphor particle PR. Thus, since it is possible to decrease the
intensity of the fluorescence propagating the binder BN, it is
possible to decrease the spread of the light emitted from the
phosphor layer 56, and by extension, from the wavelength conversion
element 51A. Therefore, it is possible to enhance the brightness in
the optical device 30 as the optical system, and thus, it is
possible to increase the optical system efficiency described
above.
Further, on the surface of the phosphor particle PR, there is
disposed the antireflection layer AR. According to this
configuration, it is possible to make the excitation light entering
the wavelength conversion element 51A easy to enter the phosphor
particles PR, and thus, it is possible to reduce the intensity of
the excitation light which is reflected by the surface of the
phosphor particle PR and fails to be converted by the phosphor
particle PR into the fluorescence. Therefore, it is possible to
enhance the wavelength conversion efficiency of the wavelength
conversion element 51A, and thus, it is possible to increase the
intensity of the fluorescence to be emitted from the wavelength
conversion element 51A compared to the wavelength conversion
element having the phosphor layer in which the phosphor particles
PR not provided with the antireflection layer AR are bound to each
other.
The method of manufacturing the wavelength conversion element
includes the layer forming step of forming the antireflection layer
on the surface of the plurality of phosphor particles, the
preparation step of preparing the mixture obtained by mixing the
plurality of phosphor particles the surfaces of which are provided
with the antireflection layers are formed and the binder including
the glass with each other, the coating step of applying the mixture
on the substrate, the calcination step of calcining the substrate
coated with the mixture, and the calcination temperature in the
calcination step is 100.degree. C. or more higher than the
softening point of the glass. Specifically, the method of
manufacturing the wavelength conversion element 51A includes the
layer forming step SA, the paste preparation step S1 and the
phosphor mixing step S2A as the preparation step, the coating step
S4, and the calcination step S6. In the layer forming step SA,
there is formed the antireflection layer AR on the surface of each
of the phosphor particles PR. In the paste preparation step S1 and
the phosphor mixing step S2A, there is prepared the mixture paste
as the mixture obtained by mixing the binder including the glass
and the phosphor particles PR provided with the antireflection
layers AR with each other. In the coating step S4, the mixture
paste is applied on the substrate 52. In the calcination step S6,
the substrate 52 coated with the mixture paste is calcined.
Further, the calcination temperature in the calcination step S6 is
100.degree. C. or more higher than the softening point of the
glass.
In other words, the method of manufacturing the wavelength
conversion element includes the layer forming step of forming the
antireflection layer on the surface of the plurality of phosphor
particles, the preparation step of preparing the mixture obtained
by mixing the plurality of phosphor particles the surfaces of which
are provided with the antireflection layers are formed and the
binder including the glass with each other, the coating step of
applying the mixture on the substrate, the calcination step of
calcining the substrate coated with the mixture, and the viscosity
of the glass in the calcination step is no higher than 10.sup.6
dPas. Specifically, the method of manufacturing the wavelength
conversion element 51A includes the layer forming step SA, the
paste preparation step S1, the phosphor mixing step S2A, the
coating step S4, and the calcination step S6 described above, and
the viscosity of the glass in the calcination step S6 is no higher
than 10.sup.6 dPas.
Modifications of Embodiments
The present disclosure is not limited to each of the embodiments
described above, but includes modifications, improvements, and so
on within the range in which the advantages of the present
disclosure can be achieved.
In the first embodiment described above, it is assumed that the
antireflection layer 55 is disposed on the first surface 541 which
the excitation light enters in the phosphor layer 54. In detail, it
is assumed that the antireflection layer 55 is disposed in
substantially the entire area of the first surface 541. However,
this is not a limitation, and it is also possible for the
antireflection layer 55 to be disposed in a range where the
incident area of the excitation light is included in the first
surface 541.
Further, it is sufficient for the antireflection layer 55 to be
disposed on the incident side of the excitation light with respect
to the phosphor layer 54, and it is also possible to dispose
another layer between the antireflection layer 55 and the phosphor
layer 54.
Further, it is assumed that the antireflection layer 55 is formed
on the first surface 541 by vapor deposition. However, the vapor
deposition is not a limitation, it is possible to provide the
antireflection layer 55 to the phosphor layer 54 using a different
method.
In the second embodiment described above, it is assumed that the
antireflection layer AR is formed so as to cover the surface of the
phosphor particle PR using CVD. However, this is not a limitation,
and the method of forming the antireflection layer AR can
arbitrarily be selected.
Further, it is not required to provide the antireflection layer AR
to all of the phosphor particles PR constituting the phosphor layer
56. In other words, providing the phosphor particle PR provided
with the antireflection layer AR is included in the phosphor layer
56, it is possible to include the phosphor particle PR not provided
with the antireflection layer AR.
In the first embodiment, it is assumed that the antireflection
layer 55 is provided to the phosphor layer 54, and in the second
embodiment, it is assumed that the antireflection layer AR is
disposed on the surface of the phosphor particle PR. It is also
possible to combine such a configuration described in the first
embodiment and such a configuration described in the second
embodiment with each other. For example, it is possible to adopt
the wavelength conversion element in which the antireflection layer
55 is provided to the phosphor layer including the phosphor
particles PR the surfaces of which are provided with the
antireflection layers AR.
In each of the embodiments described above, it is assumed that the
dimension in the X axis of the binding part B1, B2 to be bonded to
the binder BN in the surface of the phosphor particle PR is no
larger than 1/4 of the diameter of the phosphor particle PR, and
the dimension in the Y axis of the binding part B1, B2 is no larger
than 1/4 of the diameter of the phosphor particle PR. However, this
is not a limitation, and the size of the binding part B1, B2 is not
limited to the above providing the proportion of the area of the
binding part B1, B2 to the surface area of the phosphor particle PR
becomes a value no higher than 10%, and preferably becomes a value
no lower than 3% and no higher than 5%.
Further, when the dimension in the X axis and the dimension in the
Y axis of the binding part B1, B2 each become no larger than 1/4 of
the diameter of the phosphor particle PR, it is not required for
the proportion of the area of the binding part B1, B2 to the
surface area of the phosphor particle PR to become a value no
higher than 10%, or preferably become a value no lower than 3% and
no higher than 5%.
Further, it is also possible for the dimension in one of the X axis
and the Y axis of the binding part B1, B2 to exceed 1/4 of the
diameter of the phosphor particle PR.
In each of the embodiments described above, it is assumed that the
glass content rate of the phosphor layer 54, 56 is higher than 0
vol % and no higher than 10 vol %. In other words, it is assumed
that the proportion of the volume of the binder BN to the total
volume of the sum of the volumes of the phosphor particles PR and
the sum of the volumes of the binder BN is larger than 0 vol % and
no larger than 10 vol %. However, this is not a limitation, and the
proportion of the volume can exceed 10 vol % within a range in
which it is determined that the optical system efficiency is
sufficiently high. It should be noted that the proportion of the
volume is a value when manufacturing the phosphor layer 54, 56 as
described above.
In the first embodiment described above, it is assumed that the
method of manufacturing the wavelength conversion element 51
includes the paste preparation step S1, the phosphor mixing step
S2, the printing plate forming step S3, the coating step S4, the
drying step S5, the calcination step S6, the cooling step S7, and
the layer forming step S8. In the second embodiment described
above, it is assumed that the method of manufacturing the
wavelength conversion element 51A includes the layer forming step
SA, the paste preparation step S1, the phosphor mixing step S2A,
the printing plate forming step S3, the coating step S4, the drying
step S5, the calcination step S6, and the cooling step S7. However,
the method of manufacturing the wavelength conversion element is
not limited to the above, and it is also possible to eliminate any
of the steps S1 through S8, or any of the steps SA, S1, S2A, and S3
through S7. For example, the drying step S5 can be eliminated.
Further, the paste preparation step S1 and the phosphor mixing step
S2 can be executed at the same time.
In each of the embodiments described above, it is assumed that the
viscosity of the glass in the calcination step S6 is a value no
higher than 10.sup.6 dPas. In other words, it is assumed that the
calcination temperature is made 100.degree. C. or more higher than
the softening point of the glass so that the viscosity of the glass
takes a value no higher than 10.sup.6 dPas. However, this is not a
limitation, and the calcination temperature is not required to be
100.degree. C. or more higher than the softening point of the glass
to be the binder BN providing the viscosity of the glass takes a
value no higher than 10.sup.6 dPas. In contrast, when the
calcination temperature is 100.degree. C. or more higher than the
softening point of the glass, the viscosity of the glass to be the
binder BN is not required to be no higher than 10.sup.6 dPas in the
calcination step S6. In other words, it is sufficient to satisfy at
least either one of the fact that the calcination temperature is
100.degree. C. or more higher than the softening point of the
glass, and the fact that the viscosity of the glass is no higher
than 10.sup.6 dPas in the calcination step S6.
In each of the embodiments described above, there is illustrated
the reflective wavelength conversion element 51, 51A in which the
phosphor layer 54, 56 is located on the incident side of the
excitation light with respect to the substrate 52, and the
fluorescence is emitted on the incident side of the excitation
light. However, this is not a limitation, and it is also possible
to apply the present disclosure to a transmissive wavelength
conversion element for emitting the fluorescence along the incident
direction of the excitation light. In the case of the transmissive
wavelength conversion element, sapphire is preferably used as the
substrate.
Further, a dielectric multilayer film for reflecting the light
emitted from the phosphor layer 54, 56 can also be disposed between
the phosphor layer 54, 56 and the substrate 52.
In each of the embodiments described above, it is assumed that the
wavelength conversion element 51 has the configuration of being
rotated by the rotary section RT. However, this is not a
limitation, and it is also possible to adopt a configuration in
which the wavelength conversion element is not rotated. In other
words, the wavelength conversion device is not required to be
provided with the rotary section RT for rotating the wavelength
conversion element. In this case, the phosphor layer 54, 56 is not
required to be formed to have an annular shape when viewed from the
incident side of the excitation light, and can also be formed to
have, for example, a circular shape or a polygonal shape. Further,
the shape of the phosphor layer 54, 56 can also be a circular shape
or a polygonal shape when viewed from the incident side of the
excitation light irrespective of whether or not the phosphor layer
54, 56 is rotated.
In each of the embodiments described above, it is assumed that the
projector is equipped with the three light modulation devices 343
(343B, 343G and 343R). However, this is not a limitation, and the
present disclosure can also be applied to a projector equipped with
two or less, or four or more light modulation devices.
In each of the embodiments described above, it is assumed that the
projector is provided with the light modulation devices 343 each
having the transmissive type liquid crystal panel having the plane
of incidence of light and the light exit surface different from
each other. However, this is not a limitation, but it is also
possible to adopt a configuration in which the light modulation
devices each have a reflective type liquid crystal panel having the
plane of incidence of light and the light exit surface coinciding
with each other. Further, it is also possible to use a light
modulation device other than the liquid crystal device such as a
device using a micromirror such as a digital micromirror device
(DMD) providing the light modulation device is capable of
modulating the incident light beam to form the image corresponding
to the image information.
In each of the embodiments described above, there is cited an
example in which the light source device 4 is applied to the
projector. However, this is not a limitation, and it is also
possible for the light source device according to the present
disclosure to be adopted in, for example, lighting equipment, and a
spotlight or the like of a vehicle or the like. Further, the light
source device according to the present disclosure is not limited to
the configuration of the light source device 4, and providing the
light source device has a configuration provided with the
wavelength conversion element and the light source for emitting the
light which enters the wavelength conversion element, other
components constituting the light source device can arbitrarily be
changed. Substantially the same is applied to the projector
according to the present disclosure.
* * * * *